Christopher J. Fettig

Climate Change and Bark Beetles of the Western United States and Canada: Direct and Indirect Effects

Climatic changes are predicted to significantly affect the frequency and severity of disturbances that shape forest ecosystems. We provide a synthesis of climate change effects on native bark beetles, important mortality agents of conifers in western North America. Because of differences in temperature-dependent life-history strategies, including cold-induced mortality and developmental timing, responses to warming will differ among and within bark beetle species. The success of bark beetle populations will also be influenced indirectly by the effects of climate on community associates and host-tree vigor, although little information is available to quantify these relationships. We used available population models and climate forecasts to explore the responses of two eruptive bark beetle species. Based on projected warming, increases in thermal regimes conducive to population success are predicted for Dendroctonus rufipennis (Kirby) and Dendroctonus ponderosae Hopkins, although there is considerable spatial and temporal variability. These predictions from population models suggest a movement of temperature suitability to higher latitudes and elevations and identify regions with a high potential for bark beetle outbreaks and associated tree mortality in the coming century.

The Effects of Forest Fuel-Reduction Treatments in the United States

The current conditions of many seasonally dry forests in the western and southern United States, especially those that once experienced low- to moderate-intensity fire regimes, leave them uncharacteristically susceptible to high-severity wildfire. Both prescribed fire and its mechanical surrogates are generally successful in meeting short-term fuel-reduction objectives such that treated stands are more resilient to high-intensity wildfire. Most available evidence suggests that these objectives are typically accomplished with few unintended consequences, since most ecosystem components (vegetation, soils, wildlife, bark beetles, carbon sequestration) exhibit very subtle effects or no measurable effects at all. Although mechanical treatments do not serve as complete surrogates for fire, their application can help mitigate costs and liability in some areas. Desired treatment effects on fire hazards are transient, which indicates that after fuel-reduction management starts, managers need to be persistent with repeated treatment, especially in the faster-growing forests in the southern United States.

The national Fire and Fire Surrogate study: effects of fuel reduction methods on forest vegetation structure and fuels

Changes in vegetation and fuels were evaluated from measurements taken before and after fuel reduction treatments (prescribed fire, mechanical treatments, and the combination of the two) at 12 Fire and Fire Surrogate (FFS) sites located in forests with a surface fire regime across the conterminous United States. To test the relative effectiveness of fuel reduction treatments and their effect on ecological parameters we used an information-theoretic approach on a suite of 12 variables representing the overstory (basal area and live tree, sapling, and snag density), the understory (seedling density, shrub cover, and native and alien herbaceous species richness), and the most relevant fuel parameters for wildfire damage (height to live crown, total fuel bed mass, forest floor mass, and woody fuel mass). In the short term (one year after treatment), mechanical treatments were more effective at reducing overstory tree density and basal area and at increasing quadratic mean tree diameter. Prescribed fire treatments were more effective at creating snags, killing seedlings, elevating height to live crown, and reducing surface woody fuels. Overall, the response to fuel reduction treatments of the ecological variables presented in this paper was generally maximized by the combined mechanical plus burning treatment. If the management goal is to quickly produce stands with fewer and larger diameter trees, less surface fuel mass, and greater herbaceous species richness, the combined treatment gave the most desirable results. However, because mechanical plus burning treatments also favored alien species invasion at some sites, monitoring and control need to be part of the prescription when using this treatment.

Association between severity of prescribed burns and subsequent activity of conifer-infesting beetles in stands of longleaf pine

A randomized complete block experiment was performed to measure the effect of prescribed, dormant-season burns of three different levels of severity (measured as fuel consumption and soil surface heating) on subsequent insect infestation and mortality of mature longleaf pine (Pinus palustris Mill.). Multiple-funnel traps baited with a low release rate of turpentine and ethanol were used to monitor activity of certain coniferophagous beetles. Non-aggressive species, including the root beetles Hylastes salebrosus Eichhoff and H. tenuis Eichhoff, the ambrosia beetle Xyleborus pubescens Zimmermann, the reproduction weevil Pachylobius picivorus (Germar), and buprestid borers, were attracted to burned plots in numbers that correlated positively with burn severity. Beetle attraction to burned sites was greatest in the first weeks post-burn and disappeared by the second year. Two potential tree-killing bark beetles, Dendroctonus terebrans (Olivier) and Ips grandicollis (Eichhoff), were trapped in significant numbers but exhibited no attraction to burned plots. Tree mortality correlated significantly with the severity of the burns and amounted to 5% of stems in the hottest burn treatment after 3 years. The majority of the mortality was observed in the second and third years post-burn. Attacks of Ips and Dendroctonus bark beetles were apparent on nearly all dead or dying trees, and evidence suggested that root pathogens may have contributed to tree susceptibility to beetle attack and mortality. Our data indicate that selection of burn regimes that reduce or eliminate consumption of duff (e.g., favoring heading fires over backing fires) could significantly reduce mortality of longleaf pine managed for long rotations.

Ecological effects of alternative fuel-reduction treatments: Highlights of the National Fire and Fire Surrogate study (FFS)

The 12-site National Fire and Fire Surrogate study (FFS) was a multivariate experiment that evaluated ecological consequences of alternative fuel-reduction treatments in seasonally dry forests of the US. Each site was a replicated experiment with a common design that compared an un-manipulated control, prescribed fire, mechanical and mechanical + fire treatments. Variables within the vegetation, fuelbed, forest floor and soil, bark beetles, tree diseases and wildlife were measured in 10-ha stands, and ecological response was compared among treatments at the site level, and across sites, to better understand the influence of differential site conditions. For most sites, treated stands were predicted to be more resilient to wildfire if it occurred shortly after treatment, but for most ecological variables, short-term response to treatments was subtle and transient. Strong site-specificity was observed in the response of most ecosystem variables, suggesting that practitioners employ adaptive management at the local scale. Because ecosystem components were tightly linked, adaptive management would need to include monitoring of a carefully chosen set of key variables. Mechanical treatments did not serve as surrogates for fire for most variables, suggesting that fire be maintained whenever possible. Restoration to pre-settlement conditions will require repeated treatments over time, with eastern forests requiring more frequent applications.

Antennal responses of the western pine beetle, Dendroctonus brevicomis (Coleoptera: Curculionidae), to stem volatiles of its primary host, Pinus ponderosa, and nine sympatric nonhost angiosperms and conifers.

Summary.Stem volatile extracts from ten trees that are sympatric with the western pine beetle, Dendroctonus brevicomis LeConte (Coleoptera: Curculionidae) were assayed by gas chromatographic-electroantennographic detection analysis (GC-EAD). The extracts were from the primary host, ponderosa pine, Pinus ponderosa Dougl. ex Laws. (Pinaceae); two nonhost angiosperms, California black oak, Quercus kelloggii Newb. (Fagaceae), and quaking aspen, Populus tremuloides Michx. (Salicaceae); and seven nonhost conifers, white fir, Abies concolor (Gord. & Glend.) Lindl. ex Hildebr. (Pinaceae), incense cedar, Calocedrus decurrens (Torr.) Florin (Cupressaceae), Sierra lodgepole pine, P. contorta murrayana Grev. & Balf. (Pinaceae), Jeffrey pine, P. jeffreyi Grev. & Balf. (Pinaceae), sugar pine, P. lambertiana Dougl. (Pinaceae), Douglas-fir, Pseudotsuga menziesii (Mirb.) Franco (Pinaceae), and mountain hemlock, Tsuga mertensiana (Bong.) Carr. (Pinaceae). Sixty-four compounds were identified from the ten trees, 42 of which elicited antennal responses in D. brevicomis, usually in both sexes. In addition, several synthetic compounds, including a number of the antennally-active compounds from the extracted trees and some bark beetle pheromone components, elicited antennal responses in a manner similar to that observed with the extracts. Of the antennally-active compounds known to be present in trees sympatric with D. brevicomis, only geraniol was unique to its host. Four antennally-active compounds were found in the host and in other conifers; five compounds were found only in nonhost conifers; eight compounds were found in either or both of the nonhost angiosperms; eight compounds were found in either or both of the angiosperms and in nonhost conifers, but not in the host; and 19 were found in both the host and in angiosperms and/or nonhost conifers. Several bark beetle pheromone components were found in the stem volatile extracts. Conophthorin was identified from both nonhost angiosperms; exo-brevicomin was identified in A. concolor; verbenone was identified from a number of nonhost conifers; and chalcogran was identified from P. tremuloides. The number of nonhost volatile chemicals that D. brevicomis encounters and is capable of detecting, and the diversity of sources from which they emanate, highlight the complexity of the olfactory environment in which D. brevicomis forages. This provides a basis for further work related to chemically-mediated aspects of foraging in this insect and perhaps other coniferophagous bark beetles, and highlights the need to consider foraging context in the design and implementation of semiochemical-based management tactics for tree protection.

The ecology and management of moist mixed-conifer forests in eastern Oregon and Washington: a synthesis of the relevant biophysical science and implications for future land management

Land managers in the Pacific Northwest have reported a need for updated scientific information on the ecology and management of mixed-conifer forests east of the Cascade Range in Oregon and Washington. Of particular concern are the moist mixed-conifer forests, which have become drought-stressed and vulnerable to high-severity fire after decades of human disturbances and climate warming. This synthesis responds to this need. We present a compilation of existing research across multiple natural resource issues, including disturbance regimes, the legacy effects of past management actions, wildlife habitat, watershed health, restoration concepts from a landscape perspective, and social and policy concerns. We provide considerations for management, while also emphasizing the importance of local knowledge when applying this information at the local and regional level.

Response of Dendroctonus brevicomis to different release rates of nonhost angiosperm volatiles and verbenone in trapping and tree protection studies

A blend of eight nonhost angiosperm volatiles (benzyl alcohol, benzaldehyde, guaiacol, nonanal, salicylaldehyde, (E)‐2‐hexenal, (E)‐2‐hexen‐1‐ol and (Z)‐2‐hexen‐1‐ol) without [NAV] and with [NAVV] (–)‐verbenone (4,6,6‐trimethylbicyclo[3.1.1]hept‐3‐en‐2‐one) were tested at low (L), medium (M) and high (H) release rates for their ability to reduce attraction of western pine beetle, Dendroctonus brevicomis LeConte, to attractant‐baited (exo‐brevicomin [racemic, 3 mg/d], frontalin [racemic, 3 mg/d] and myrcene [18 mg/d]) multiple funnel traps. NAV‐L (40 mg/d) had no significant effect. Verbenone alone (50 mg/d) and NAV‐M (240 mg/d) both significantly reduced attraction, but no significant difference was observed between the two treatment means. NAV‐H (430 mg/d) significantly reduced catches by ∼60% and 78% compared to verbenone alone and the baited control, respectively. In a second experiment, combining (–)‐verbenone with NAV (NAVV) increased the effects observed in Experiment 1. NAVV‐M (240 mg/d) resulted in an ∼69% and 83% reduction in trap catch compared to verbenone alone and the baited control, respectively. Significantly fewer D. brevicomis were captured in NAVV‐H (430 mg/d) than any other treatment resulting in an ∼93% reduction in trap catch compared to the baited control. In a third experiment, NAVV was tested at three release rates for its ability to protect individual ponderosa pines, Pinus ponderosa Dougl. ex Laws., from attack by D. brevicomis. Cumulative release rates varied in direct proportion to tree diameter, but represented quarter, half and full NAVV rates. NAVV significantly reduced the density of D. brevicomis attacks, D. brevicomis successful attacks, and levels of tree mortality on attractant‐baited trees. Only three of 15 NAVV‐treated trees died from D. brevicomis attack while ∼93% mortality (14/15) was observed in the untreated, baited control. Quarter and half rates were ineffective for reducing tree mortality.

Evaluation of Multiple Funnel Traps and Stand Characteristics for Estimating Western Pine Beetle-Caused Tree Mortality

ABSTRACT The western pine beetle, Dendroctonus brevicomis LeConte (Coleoptera: Curculionidae: Scolytinae), is a major cause of ponderosa pine, Pinus ponderosa Dougl. ex Laws., mortality in much of western North America. This study was designed to quantify relationships between western pine beetle trap catches [including those of its primary invertebrate predator Temnochila chlorodia (Mannerheim) (Coleoptera: Trogositidae)], and levels of tree mortality attributed to western pine beetle at 44 trapping sites (stands) and within five general locations (forests) in California. Furthermore, we evaluated relationships between forest stand characteristics and levels of western pine beetle-caused tree mortality. Preliminary analyses were conducted by Pearsons correlation coefficient (r) using tree mortality per hectare and percentage of tree mortality and 10 potential predictor variables. All predictor variables that had significant correlations (western pine beetle per day, western pine beetle: T. chlorodia, percentage of western pine beetle [percentage of total trap catch represented by western pine beetle], trees per hectare, basal area of all tree species, basal area of P. ponderosa, mean diameter at breast height [dbh] and stand density index) were considered for linear and multiple linear regression models for predicting levels of western pine beetle-caused tree mortality. Our results suggest monitoring western pine beetle populations through the use of pheromone-baited multiple funnel traps is not an effective means of predicting levels of western pine beetle-caused tree mortality. However, levels of western pine beetle-caused tree mortality can be efficiently predicted (adjusted R 2 >0.90) at large spatial scales (forests; ≈3,000–14,000 ha of contiguous host) by simply measuring stand density, specifically the basal area of all tree species or stand density index. The implications of these results to forest management are discussed.

Trap Lure Blend of Pine Volatiles and Bark Beetle Pheromones for Monochamus spp. (Coleoptera: Cerambycidae) in Pine Forests of Canada and the United States

ABSTRACT In 2007–2008, we examined the flight responses of Monochamus titillator (F.) complex [M. titillator, Monochamus carolinensis (Olivier), and any possible hybrids], Monochamus scutellatus (Say), Monochamus clamator (LeConte), Monochamus obtusus Casey, and Monochamus mutator LeConte (Coleoptera: Cerambycidae) to multiple-funnel traps baited with and without host volatiles and bark beetle pheromones. Experiments were conducted in mature pine (Pinus) stands in Alberta (Canada), and Arkansas, Arizona, California, Florida, Idaho, Michigan, Montana, New Hampshire, North Carolina, Ohio, Oregon, Tennessee, Utah, and Wisconsin (United States). At each location, traps were deployed in 10 replicate blocks of four traps per block. The trap treatments were: 1 ) blank control; 2) ipsenol and ipsdienol; 3) ethanol and &agr;-pinene; and 4) a quaternary blend of ipsenol, ipsdienol, ethanol, and &agr;-pinene. All five species or species complex of Monochamus preferred traps baited with the quaternary blend over all other treatments. The consistency of these results across such a large geographic area suggests that similar selection pressures may be acting on Monochamus spp. in pine forests, regardless of variation in stand composition and climatic conditions. Our results suggest that multiple-funnel traps baited with the quaternary blend of ipsenol, ipsdienol, ethanol, and &agr;-pinene may be highly effective for monitoring various Monochamus spp. in pine forests of North America, and may have utility in trapping and detection programs in North America and overseas.